Water contamination is a world-wide problem afflicting both developed and emerging countries. A large contributor to water contamination is the pulp and paper industry. For example, the pulp and paper industry is regarded as the third most polluting industry in North America. The production of paper can have a number of adverse effects on the environment. For example, waste water effluent from a pulp and paper mill may contain toxic inks, dyes and polymers in addition to solids, nutrients, and dissolved organic matter such as lignin. These contaminants frequently find their way into rivers, lakes, and other bodies of water. Moreover, used or discarded paper is a major component of many landfill sites, where paper waste can comingle with groundwater. Even paper recycling can be a source of pollution due to the sludge produced during deinking.
Some techniques currently in use for removing ink and other contaminants include introducing chemical agents to contaminated water in order to cluster and remove particulate matter. In one technique, chemical flocculants are added to water, for example, ferric chloride or ferric sulphate. The resulting flocs can be more readily filtered. In another technique, the photodegradation of titanium dioxide responsive to UV radiation is used to generate free radicals in water. The free radicals can then oxidize organic chemicals. However, these conventional techniques require adding chemical agents or other additional matter such as metal oxides to the water to be decontaminated.
Other conventional techniques include using electricity to cluster contaminants for separation. In one technique, hydrolysis is used to generate bubbles having a negative charge. The bubbles can be selectively targeted at specific particles by leveraging the zeta potential of the particles. In another technique, electrolysis is used to produce coagulating agents, such as metal hydroxides. The coagulating agents can combine with pollutants to form large flocs. Yet another conventional technique involves the creation of atmospheric liquid plasma, for example, by electric discharge, in order to treat or degrade contaminants. However, these conventional techniques typically require discharges of extremely high energy or the injection of gas or air bubbles into the system.